Enfold Systems has announced the release of Server 2.0 Beta, which promises full integration of Plone with Active Directory. I currently have an installation of Plone running on a Windows server with partial AD integration using Group User Folder (GRUF). It permits authentication and the use of LDAP groups for sharing permissions (sometimes with difficulty) but does not allow the same operations at the individual user level. Unfortunately, it looks as if the product will cost about $2000, which is a lot to pay for Windows integration when the base install of Plone is free. How badly do we want full AD integration? Probably not this badly.
Enfold Systems is the for-profit company of a handful of Plone biggies, including the founder. It competes with other open-source content management systems such as Mambo and PHP-Nuke.